Laboratory and field performance of silane anti-strip agent

ARIZONA DEPARTMENT OF TRANSPORTATION
REPORT NUMBER: FHWAIAZ EP 8101
LABORATORY AND FIELD
PERFORMANCE OF SILANE
ANTI-STRIP AGENT
Final Report
Prepared by:
Chaouki A. Gemayel
Arizona Transpoltation Research Center
November 1986
Prepared for:
Arizona Department of Transportation
206 south 17th Avenue
Phoenix, Arizona 85007
in cooperation with
U.S. Department of Transportation
Federal Highway Administration
The contents of this report reflect the views of the authors who are responsible for
the facts and the accura of the data presented herein. The contents do not
necessarily reflect the o2 cial' vie.ws or policies of the Arizona Department of
Transportation or the Federal Highway Administration. This report does not
constitute a standard, specification, or regulation Trade or manufacfarer's names
which may aP pear hereln are cited only because they are considered essential to the objectives o the report. The U. S. Government and the State of Arizona do not
endorse products or manufacturers.
TECHNICAL REPORT DOCUMENTATION PAGE
I. REPORT NO. 1 2. GOVERNMENT ACCESSION NO. I 3. RECIPIENT'S CATALOG NO. 1
AZ8101
4. TITLE AND SUBTITLE
LABORATORY AND FIELD PERFORMANCE OF SILANE ANTI-STRIP
AGENT
16. ABSTRACT
A previous ADOT research p r o j e c t resulted i n strong evidence t h a t the use o f I organo-silane as an asphalt a d d i t i v e was very e f f e c t i v e i n preventing s t r i p p i n g i n
asphalt concrete pavements. A t e s t section approximately 2800 ft long and 12 ft wide
incorporating a silane agent, Oow Corning 990, was placed on,the crossroad o f the east
I Williams T. I. on SR 64 between MP 185.3 and 185.7 i n October 1981 t o v e r i f y t h a t claim
Pave Bond Special (PBS) a n t i - s t r i p agent was used on the remaining portion o f the
- roadway. The PBS sections d i r e c t l y adjacent t o the silane t e s t section were designate
I as control sections.
I n January 1984, visual observations o f the silane t e s t section indicated t h a t the
pavement surface experienced s l i g h t r a v e l i n g throughout the section and moderate t o
severe raveling a t several l o c a l i z e d areas. The PBS control section was i n e x c e l l e n t 1 condition. The experimental t e s t section was overlayed by 1" ASCS i n October 1984
which prevented f u r t h e r f i e l d evaluation.
Laboratory tests were conducted on asphalt concrete samples obtained a t the time
I of c o n s t r u c t i o n and on cores taken from t h e s i l a n e and PBS sec t ions 5 months and 3 years after construction. The r e s u l t s showed t h a t the PBS t r e a t e d m a t e r i a l have
superior properties. However, several factors made the r e s u l t s questionable:
difference i n b u l k d e n s i t i e s between PBS and silane cores, clay material was observed I i n both mixtures and therefore increasing the moisture s u s c e p t i b i l i t y , and long delays
between the time the cores were d r i l l e d and the time they were tested.
Because o f the l i m i t e d f i e l d evaluation and the l i m i t a t i o n s on the v a l i d i t y o f the I laboratory r e s u l t s , no major conclusions can be drawn regarding t h e effectiveness o f
the silane i n preventing s t r i p p i n g .
17. KEY WORDS 18. DISTRIBUTION STATEMENT I Asphalt concrete, Stripping, Debonding, I A n t i - s t r i p aqent, Asohalt a d d i t i v e ,
5. REPORT DATE
November 1986
6. PERFORMING 0RGANIZAT;TIOH COO€
7 AUTHOR&)
Chaouki A. Gemayel
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arizona Transportation Research Center
Mail Drop 075R
206 South 17th Avenue; Phoenix, Arizona 85007
12. SWNSORING AGENCY NAME AND ADDRESS
Federal Highway Administration
234 North Central Avenue, Suite 330
Phoenix, Arizona 85004
. -
I Silane.
8. PERFORMING ORGANIZATION REPORT NQ
10. WORK UNIT NO.
11. CONTRACT OR GRANT NO.
HPR-PL-l(31) Item 116
I3.PIPE OF REWRT a PERIOD COVERED
Final Report
October 1981-November 1986
14. SPONSORING AGENCY CODE
- IS. SUPPLEMENTARY NOTES
EXPERIMENTAL PROJECT
A28101
LABORATORY AND FIELD PERFORMANCE OF
SILANE ANTI-STRIP AGENT
NOVEMBER 15,1986
PREPARED BY:
CHAOUKI A. GEMAYEL
TABLE OF CONTENTS
PAGE
TECHNICAL DOCUMENTATION ............................................................... i
TABLE OF CONTE.N...T...S.... ................................................................................................................................................................. ...... i.i. . LIST OF FIGURES n..i. LIST OF TABLES ................................................................................................ 1u INTRODUCTION ................................................................................................. 1
OBJECTIVE ........................................................................................................... 1
MECHANISMS OF STRIPPING ....................................................................... 2
PRODUCT DESCRIPTION ............................................................................... 2
CONSTRUCTION REPORT. ............................................................................3
PRODUCT EVALUATION PLAN ................................................................ 4 LABORATORY EVALUATION ...................................................................... 4
FIELD EVALUATION ........................................................................................ 6 CONCLUSIONS AND RECOMMENDATIONS. .......................................... 7
REFERENCES ...................................................................................................8...
APPENDICES
TEST SECTION PLANS .....................................................................A...1..
TEST SECTION PHOTOS ....................................................................B.. 1
LABORATORY DATA .........................................................................C.. 1
RESEARCH WORKPLAN ..................................................................... Dl
LIST OF FIGURES
FIGURE: PAGE
1 LOCATION OF THE EXPERIMENTAL TEST SECTION ......... A1
2 TYPICAL PAVEMENT CROSS SECTION ..................................... A2
3 SILANE TEST SECTION - LOOKING SOUTH
TABLE:
1
2
- - - ~ - - - - ---
FROM STA 3013+00 (JANUARY 1984) .......................................... B1
SILANE TEST SECTION - LOOKING SOUTH FROM STA 3015 + 00 (JANUARY 1984) .......................................... B1
PBS TEST SECTION - LOOKWG SOUTH FROM STA 3015 + 00 (JANUARY 1984) .......................................... B2
SILANE TEST SECTION - SURFACE TEXTWE (JANUARY 1984) .................................................................................. B2
SURFACE TEXTURE OF BOTH PBS (OUTSIDE LANE)
AND SILANE (INSIDE LANE) (JANUARY 1984) ....................... B3
1" ACSC OVERLAY - LOOKING NORTH FROM STA 3021 + 70 (AUGUST 1985) ............................................. B3
1" ACSC OVERLAY - LOOKING NORTH FROM STA 3033 + 87 (AUGUST 1985). ............................................ B4 1" ASCS OVERLAY - SURFACE TEXTURE. ................................ B4
LIST OF TABLES
LABORATORY EVALUATION OF SILANE
PRODUCTlON SAMPLES ..................................................................
LABORATORY EVALUATION OF PAVE BOND ~- - - - - SPECIAL (PBS) PRODUCTION SAMPLES ................................... C2
RESILIENT MODULUS EVALUATION OF PBS
AND SILANE PRODUCTION SAMPLES ...................................... C3
LOCATION 01 F CORES TAKEN IN MARCH 10, 1982 ................ C4
STAINED IN MARCH 1982 ......................... C6
LABORATORY EVALUATION OF PBS CONmOL
SECTION CORES OBTAINED IN MARCH 1982 ......................... U
LABORATORY EVALUATION OF SILANE TEST
SECTION CORES OE
LOCATION OF CORES TAKEN IN JANUARY /
FEBRUARY 1985 ................................................................................ C7
VOIDS ANALYSIS OF PBS AND SILANE CORES
.
OBTAINED IN JANUARY 1985 ........................................................ C9
AVERAGE TEST RESULTS FOR LABORATORY
EVALUATION OF P-B- S- -A-N -D SILANE CORES
. JANUARY 1985. .......................................................C 10
INTRODUCTION
An asphalt concrete pavement is inherently dependent upon the cohesive and
adhesive characteristics of the binder to hold it together. As a result, the bond between the
asphalt binder and the mineral aggregate is of special importance. It is critical that good
bond is developed during construction and maintained for the life of the pavement. Any
degree of loss of the asphalt-aggregate bond will result in a corresponding loss of pavement
performance in one manner or another. The strength of an asphalt concrete mvtture is a
result of the cohesive resistance of the binder, the adhesive bond between the binder and
the aggregate, aggregate interlock and frictional resistance between aggregate particles.
Under certain circumstances, an asphalt binder will separate from the aggregate, a
complex phenomenon known as debonding (commonly referred to as stripping).
Debonding is a function of the environmental conditions, traffic loading, binder and
aggregate characteristics, mixture properties and more. Even though a proper bonding of
the asphalt to the aggregate may take place during construction, debonding n still possible.
Water intrusion is the mechanism that will facihtate debonding by replacing the asphalt
coating on mineral aggregates. Since water will always be present m one form or another,
stripping is always a possibility. A brief review of the mechanisms of stripping is presented
in a subsequent section of this report.
Failure caused by stripping occurs in two stages: the first stage is the breaking of the
adhesive bond between the aggregate surface and the asphalt cement. The second stage is
failure of the pavement under traftic (1). If stri ping within the pavement becomes
excessive, loss of strength may result in excessive de? or mations caused by repeated loading.
Failure caused by stripping can also result in cracking and surface raveling of the
pavement.
Several methods have been used to limit the possibility of stripping. Some of the
more common methods are:
1. The addition of dry lime or portland cement in small percentages to the mix
or lime slurry treatment of mineral aggregate,
2. Precoating aggregates with bitumen prior to asphalt concrete production,
3. The addibon of selected natural mineral fillers,
4. Disallowance of lmown hydrophilic aggregates,
5. Washing, wasting or blending of aggregates, and
6. The addition of chemical anti-stripping agents.
AU of these methods, for one reason or another, are not always acceptable or
economical in every situation.
OBJECTIVE
A previous ADOT research project (HPR-PL-l(19) Item 178) entitled "An
Evaluation of Chemical Coupling Agents to Control Debonding of Asphalt from
Aggregates" resulted in strong evidence that the use of organo-silanes were very effective in
preventing stripping of asphalt by action of moisture (2). To complement the laboratory
investigabon, a construction experimental project was approved to establish a test section
of asphalt concrete utilizing an Amino functional organo-silane as a stripping preventative.
The urpose of the test section was to com are the performance of an organo-silane known as 8ow Coming 990 against Pave Bon Special, an asphalt additive commonly
utilized by ADOT.
B
MECHANISMS OF STRIPPING
Taylor and Khosla (1) indicated in their report that as many as five different
mechanisms have been blamed for the loss of bond between the aggregates and the asphalt
binder. A brief summary of those mechanisms is given below.
Detachement:
Detachement is the separation of an asphalt film from an aggregate surface by a
thin layer of water, with no obvious break in the asphalt film. The asphalt film can be s
peeled cleanly from the aggregate indicating a complete loss of adhesion
Displacement:
In this mechanism, water penetrates to the aggregate through a break in the asphalt
film. This break can be caused by incomplete coating of the aggregate initially, by film
rupture, or by pinholes in the asphalt film which can form after coating dusty aggregates.
Spontaneous Emulsification: -
Water and asphalt combine to form an inverted emulsion where asphalt represents
the continuous phase and water represents the discontinuous phase. The presence of
emulsifiers such as mineral clays and some asphalt additives can aggravate further the
stripping problem.
Pore Pressure:
Pore pressure has been suggested as a mechanism of strippin& in .hig h void mixes
where water may circulate freely through interconnected voids. Dens caoon due to traffic
may entrap some water in the voids. Further traffic can cause high water pressure which
could lead to the loss of adhesion between the aggregates and the binder.
Hydraulic Scouring:
This mechanism is only applicable to surface courses. Stripping results from the
action of traffic tires on a saturated pavement surface. This causes water to be pressed
down in front of the tire and immediately sucked away from the pavement behind the tire. -
It has been indicated that stripping begins at the bottom of the asphalt bound layer
and progresses upward to the top of the layer. This is true because the lower portion of the
layer is under tension. This could lead to the rupture of the asphalt film causing water
intrusion and therefore increasing the possibility of stripping.
PRODUCT DESCRIPTION
Pave Bond Special:
Pave Bond Special (PBS) is a registered trade name of a Carstab Corporation
product. It is marketed as an asphalt additive to prevent debonding. This product was
extensively used by ADOT prior to the modification of the asphalt concrete mix design
procedures in 1982. Currently this product is an approved anti-strip agent for asphalt
concrete friction courses.
Dow Coming 990:
Silane coupling agents were first introduced to improve the water resistance of
reinforced plastics. It was soon observed that they also imparted significant improvement
to initial properties of laminates (3). Hydrophilic mineral surfaces were used in preparing
composites with organic polymers and silane was used to improve the bond. The similarity
between the polymer-glass systems and the pavement materials was noted and it was felt
that silanes may have the potential to increase the bond between asphalt and mineral
aggregate surfaces.
The original product used in the initial laboratory study under HPR-PL-l(19) Item
178 was known as Dow 2-6020. It was a registered trade name of DOW Corning. It was
primarily used as a coupling agent for the resin and plastic industry (3). It is a low viscosity
liquid of the type: aminoalkyl functional silane with the molecular formula
(CH30)3SiCH2NHCH2CH2NH2. It is only one member of one subclass of the much
larger group of functional organo-silane coupling agents.
Dow 2-6020 was not initial1 marketed for the highway industry. However, the
same product was later renamed to &ow Corning 990 and identified as an asphalt additive.
According to the manufacturer's information, Dow Corning 990 additive is effective as an
anti-stripping agent at low concentrations (0.5 - 1.0 lb per 1000 lb bitumen). The exact
quantity added depends on the nature of the particular asphalt mix. A uniform blend is
important and can be accomplished by metering the additive directly into the mixing system
of an asP halt plant or by adding it to filled tank trucks and recirculating through a bypass system or at least 20 minutes for each of the 1000 gallons of asphalt. A third option
available to the contractor is the pretreatment of the aggregate with the additive.
CONSTRUCTION REPORT
The experimental test section is located on the crossroad of the East Williams T.I.
on SR 64 between mile posts 185.3 and 185.7. The test section was established by a change
order (C.O. # 28) on project I-IG-40-3 (28). This construction experimental feature
consisted of adding two-tenths of one percent silane by weight of the asphalt and placing
the treated asphalt concrete in a section of pavement that is approximately 2800 feet in
length. Two test areas were constructed:
1. Section A is located on the northbound lanes between station 3027+40 and
station 592+72 (3046+36.62=593+55.63). The 1980 feet long by 12 feet
wide section was placed in the inside travel lane near the centerline of the
highway.
2. Section B is located on the southbound shoulder and a part of the outside
travel lane between station 3013+73.62 and Station 3021 +70. The width of
the section varied between 8 and 14 feet (8 ft between sta 3013+73.62 and
sta 3016+50,8 to 14 ft taper section between sta 3016+50 and 3018+00, and
14 ft between 3018+00 and 3021+70).
The location of the test section was selected in the Williams area because of the
past history of stripping problems along 1-40 in the Williams, Flagstaff and surrounding
areas. Stripping has been reported in pavement shortly after the completion of
construction activities even when anti-strip agents were used.
The project location and geomerty are shown in Fig. 1 and 2. The size of the section
was adequate for field testing and evaluation. The remainder of the project was
constructed using PBS, the anti-strip agent originally specified in the construction project.
The sections containing PBS and which are directly adjacent to the silme test sections were 7
designated as control sections.
A total of 872.85 tons of asphalt concrete containing the silane was used for this
experiment. The silane treated material was placed in the top 2 inch lift of the surface
course. The pavement structural components are also shown in Fig. 2. The application
rate of the silane was ap roximately 0.20 % silane by weight of the asphalt cement. The
test sections were place 8 on October 14, 1981. There were no problems associated with
placing and compacting the pavement. .
i
Although it was suggested by research ersonnel that three ranges of silane concentrations be tested (0.05 %, 0.15%, and 0. 2 % by the wei ht of asphalt), only one
could be estimated (0.20%) due to problems with metering the ow concentration of the
silane additive.
f
PRODUCT EVALUATION PLAN
The research workelan submitted by the Arizona Transportation Research Center
(ATRC) to the Federal Jibghway Administration (FHWA) indicated that the evaluation of
the experimental section will consist of conducting laboratory testing on the treated asphalt
concrete in both the experimental and control section. A copy of the workplan is enclosed
in appendix D.
The tests were to be conducted during construction (i.e. sampled material prior to
placement and compaction) and at several stages during the life of the pavement. In
addition, the evaluation included visual determination of stripping (if any).
?
LABORATORY EVALUATION
The laboratory testing rogram consisted of the evaluation of properties that would
reflect the moisture susceptitility of the asphalt concrete mixture. These properties
included the strength retention ratios as estimated from the immersion-compression and
dynamic stripping tests, conventional mix desigo properties (i.e. Marshall and Hveem
parameters), and the determination of the asphalt brnder viscosity to study the effect of the
additives on the aging of the binder. The laboratory evaluation consisted of a series of tests
that were conducted at three stages within the service life of the pavement. Tests were
performed on the treated mixture sampled during construction and on cores obtained from
the field 5 months later and 3 years later. 4
Material Sampled During Construction:
The tests listed below were conducted on both the PBS and silane field mixtures
obtained prior to compaction:
A) Immersion-compression, Marshall stability and flow, Hveem stability and
cohesion, and viscosity of extraction binder.
B) Resilient modulus on Hveem compacted specimens when
conditioning with the hydraulic device. The test is continued undt'r faainludr ea. fter
Part A of this program was completed on January 22,1982. Part B was delayed until
July 9, 1982 due to equipment malfunctions. The results of both parts are shown in Tables
1 to 3.
Cores Obtained After Five Months:
Field samples were obtained on March 10, 1982 from the experimental and control
sections. Twenty cores were taken at random in each section. The location of the cores
are included in Table 4. The tests conducted on these sam~lesin cluded the immersion-compression,
resilient modulus tests on original and cohditioned cores, and visual
determination of stripping. The results of these tests are presented in Tables 5 and 6.
Cores Obtained After Three Years:
Field samples were taken again after the pavement had been in service for three
years. A total of eighty four cores were drilled. Some of the cores were drilled next to the
1982 locations and the remaining were selected at random in both the control and
experimental sections. The location of the cores are included in Table 7. The coring
operation began in January 9-10,1985 and was completed in February 12-14,1985.
A comprehensive testing program was performed on the cores selected from both
the control and the experimental section The tests included the resilient modulus
evaluation, Hveem and Marshall tests on both the original and remolded cores and binder
extraction on both PBS and silane mixtures. The test program was completed in April 24,
1986. The results are listed in Tables 8 and 9.
Discussion of Laboratory Results:
The results of tests performed on the samples obtained from the field during
construction showed a slight difference between the properties of both the silane and PBS
treated mixtures. The silane mixture showed slightly higher stability values which might be
attributed to the difference in the average bulk density. Although the silane mixture
exhibited a higher wet strength, the strength retention ratio obtained from the immersion-compression
test was a little higher for the PBS samples.
Higher resilient modulus values were obtained for the dry specimens containing the
silane treatment. The specimens containing both the PBS and silane treated material
cracked after conditioning. Note that the resilient modulus tests were delayed for
approximately six months after the completion of the first part of the testin rogram. In
addition, a substantial amount of clay was observed throughout the mix. erefore the
results should be reviewed with caution.
+Fl
The results of the tests conducted on the cores obtained in March of 1982 are listed
in Tables 5 and 6. Visual observation during testing revealed obvious weakening of cores
after exposure to moisture. The weakening was observed as cracking and small eruptions
in the cores. Closer examination of the cores showed clay balls to be the cause of the
distress. The presence of clay was also noted in the production samples which were tested
earlier. The influence of the clay on the results of the tests conducted on the cores limits
the validity of any conclusions drawn on the performance of the two additives.
The results indicated that the PBS cores showed superior properties to the silane
cores. Strength retention values from both the immersion compression and dynamic
stripping were higher for the PBS specimens.
Similar visual observations were made on the cores obtained in 1985. Clay material
was observed throughout the mix. Another factor limiting the validity of using these test
results to compare the performance of the two additives is the long delay experienced z
between obtaining the cores and the completion of the testing program (approx. 15
months). To complicate the matter further, the cores showed consistently higher densities
in the PBS section. The results of the tests indicated that the PBS have superior properties.
It is not known to what extent the difference in the densities had on these results. Voids
calculations showed higher air voids in the silane section. Air voids in both the silane and
PBS cores were higher than the expected design air voids as obtained by the Marshall and
Hveem methods. Note that the higher air voids in the mixture, the higher chance for water
intrusion and therefore the higher moisture susceptibility of the mixture. This could
explain some of the difference between the properties of both PBS and silane mixtures. i
Absolute viscosity tests conducted on extraction binders from cores obtained in
January 1985 indicated the silane agent increases the viscosity of the asphalt binder. This
increase in viscosity may result in a decrease in the flexibility of the pavement and
therefore a decrease in the pavement serviceability due to possible fatigue cracking.
In conclusion, although the PBS cores indicated higher stripping resistance as shown
by the higher strength retention ratios for tests conducted on the original mixtures as well
as the cores, it is hard to rank one product over another. The difficulty arises from
different factors which include the presence of clay material in both mixtures, the -
difference in densities between the PBS and silane cores, and the delay in testing the cores
after obtaining them.
FIELD EVALUATION
The project suffered a delay in inspection reportin until January, 1984 when the
test section was visuall inspected and photographed (Fig. f -7). The control sections were in excellent condition (kg8.) with no apparent visual distresses. 7
Fine particle erosion was observed in the silane test areas. Slight raveling was
visible throughout test area A The fine particles were eroded leaving the coarse
aggregates exposed (Fig. 6 & 7). On the other hand, test area B showed more localized
raveling of higher severity than that observed in section A (Fig. 3 & 4). The distressed
areas in test area B were located near the construction joint between the silane and the
PBS test sections.
The original avement design required an 8 1/2 in. thick asphalt concrete surface course and 1/2 in. tll'c k asphalt concrete friction course (ACFC) be placed on to of the A
10 in. awegate base. The friction course was to be placed the following fall. If owever,
the friction course was later deleted and the thickness of the surface course was reduced by
1/2 in. (C.O. # 24 project I-IG-40-3(28)). This action was taken by the Materials section
because of problems experienced with the open-graded friction courses in a freeze-thaw
environment (4). These problems were more visible in areas that were not exposed to
sunlight because of ice accumulation. This condition is typical of that existing in the
premises of the experimental project.
The reduced thickness was replaced by a 1 in. thick asphalt concrete dense mix
overlay with a 1/2 " maximum aggregate size. The overlay was placed under project I-IG-
40-3(58) which was completed in October of 1984. Portland cement was used in the 1 inch
overlay to prevent stripping.
The presence of the overlay revented ATRC's personnel from visually comparing
the strip ing potential of the contro ? and experimental sections. A visual field ins ection
in August of 1985 to evaluate the condition of the pavement al t'e r the
placed (Figure 9-11). No signs of distress were observed other than two
transverse cracks extending across the fu!l width of the pavement at the beginning and end
of the test section.
No major conclusions could be drawn for the purpose of comparison between the
experimental and control section based on the available field inspection reports.
CONCLUSIONS AND RECOMMENDATIONS
The results of laboratory tests conducted at different stages during the three year
evaluation period suggest that PBS has su erior properties. However, the reliability of
these results is questionable due to several !ac tors: a difference in the bulk densities of the
cores obtained from the test sections was experienced with PBS cores consistently
exhibiting higher densities, clay material was observed in all mixtures increasing the
moisture susce tibility, and long delays were experienced between the time the cores were
obtained and t g e time they were tested.
The field evaluation indicated a sli ht to moderate raveling of the fine particles in
the silane test sections. The long term pe ormance of the additives could not be obtained
since both sections were overlayed.
r!
In conclusion, the corn arison of the PBS and silane anti-strip additives are
inconclusive and would not &ct current ADOT spedcations. At the present time,
ADOT uses liquid anti-strip agents on ACFC mixes. Several products are included on the
Material's ap roved products list. Portland cement and lime are currently used to control
stripping in cf ense mixtures. Usually, 1 to 2 % by weight of the mineral aggregates are
added to original mixes and 1 % by weight of virgin and salvaged material are added to
recycled asphalt concrete.
Further laboratory and field testing will be required before recommendations could
be made as to whether or not this product should be included in the anti-strip agents'
approved list.
REFERENCES
1) Joseph A. Di Vito and Gene R. Moms, "Silane Pretreatment of Mineral Aggregate
to Prevent Stripping in Flexible Pavements" A Paper Presented at the Annual
Meeting of the Transpo.tation Research Board - Washington, D.C.; January 1982. i
2) M. A Taylor and N. P. Khosla, "Stripping of Asphalt Pavements: State of the Art",
Transportation Research Record 911, Transportation Research Board -
Washlngton,D.C.; 1983.
3) Plueddemann, E. P ., "Mechanism of Adhesion of Coatings Through Reactive
Silanes", Journal of Paint Technology, March 1970.
4) Personal communications with Mr. Donald Dorman of ADOTs District 4.
APPENDIX
$7
-3
STA. 3013 + 73.62
EAST WILLIAMS
CROSSROAD
4 EAST WILLIAMS CROSSROAD
END SILANE
SECTION "0"
STA. 3021 + 70
END SILANE
STA. 592 + 75
STA. 5 8 4 + 75
END I" AC ( 1/21
FIGURE 1: LOCATION OF THE EXPERIMENTAL TEST SECTION
-Al-
SILANE TREATED
MIXTURE (2" LIFT) 7 OVERLAYED 10,1984
8" A.C.
10" S. M.
DETAIL A-A
I W' varies from 8 t o 14 f e e t
FIGURE 2: TYPICAL PAVEMENT CROSS SECTION
SILANE
Marshall Method Bulk Density Stability Flow
(PCf (lbs)
Hveem Method Bulk Density, pcf Stability Cohesion
A 146.2 26 81
B 145.9 2 7 105
C 146.5 -2 9 -107
AVg . 146.2 2 7 98
Extraction Results Gradation
Sieve % Pass
% Bitumen
Abs. Viscosity @ 140'~.
4.96
3440 poises
Immersion compression Results*
D r v Strensth. vsi Wet Strensth. vsi % Retention
70 234 33
Ava. Density of Svecimens 142.5 pcf
* Upon failure of specimens, the interior and exterior
was observed to have a substantial amount of clay
present throughout the mix.
TABLE 1: LABORATORY EVALUATION OF SILANE PRODUCTION SAMPLES
PAVE BOND SPECIAL
Marshall Method Bulk Density Stability Flow
(pcf (lbs)
A 145.1
B 146.1
C 145.2
avg . 145.6
Hveem Method Bulk Density, pcf Stability Cohesion
A 146.9
B 145.8
C 145.9
avg . 146.2
Extraction Results Gradation
Sieve % Pass
1" 100
3/4 9 9
1/ 2 86
3/8 80
1/4 6 9
4 6 3
8 4 6
10 4 1
16 32
30 24
40 19
5 0 13
100 6
200 4.1
% Bitumen 5.47
A~S. viscosity @ 140'~. 2860 poises
Immersion Compression Results*
D m Strensth. wsi Wet Strenath. ~ s i % Retention
555 217 39
Ava. Densitv of Swecimens 141.5 pcf
* Upon failure of specimens, the interior and exterior
was observed to have a substantial amount of clay
present throughout the mix.
TABLE 2: LABORATORY EVALUATION OF PAVE BOND SPECIAL
PRODUCTION SAMPLES
SILANE
-
i
PAVE BOND SPECIAL
*liveem compacted
NOTE: All specimens cracked after conditioning.
TABLE 3: RESILIENT MODULUS EVALUATION OF PAVE BOND SPECIAL
AND SILANE PRODUCTION SAMPLES
CORE #
rnCATION
M.P. or STA. R-L
592+75 R5
3043+38 L8
3042+56 L6
3041+86 L5
3040+61 L11
3039+61 L6
3938+61 L4
3038+16 L7
3037+00 L7
3034+00 L5
3014+00 R i 3
3014+50 R12
3015+00 R14
3016+50 R12
3017+00 R11
3017+50 R12
3018+00 R12
3019+00 R12
3020+00 R12
3021+00 R12
529+75 L12
3043+36 R8
3042+56 R12
3041+86 R14
3040+61 R14
3034+61 R14
3038+61 R16
3038+16 R15
3037+00 R15
3034+00 R14
3014+00 L13
3014+50 L12
3015+00 L12
3016+50 L13
3017+00 L12
3017+50 L10
3018+00 L10
3019+00 L12
3020+00 L15
3021+00 L15
DEPTH
10.2
9.0
9.5
9.5
8.5
10.5
9.5
9.0
9.5
9.7
9.5
9.0
9.6
9.5
9.6
9.3
9.6
10.5
9.3
10.5
9.0
9.5
9.0
9.0
9.0
9.5
9.5
9.5
9.5
9.0
9.7
9.5
9.0
9.8
10.0
10.1
10.0
9.5
9.5
9.0
NOTE: CORES No. 1 THRU 20 WERE TAKEN FROM THE SILANE TEST
SECTION. CORES 21 THRU 40 WERE TAKEN FROM THE PBS
CONTROL SECTION.
TABLE 4: LOCATION OF CORES TAKEN I N MARCH 10,1982
PAVE BOND SPECLQL
Core #
Core #
Immersion Compression
Unit Wt. f~cfl_ Comvressive Load I lb)
146.0 6420
144.2 6280
142.0 5480
144.1 6060
Strength = 482 psi
Wet Strenuth
Unit Wt. fvcf) Comuressive Load f lbl_
143.0 3780
143.5 4480
145.6 -5860
144.0 4707
Strength = 375 psi
% Retention = 78
Dynamic Stripping
D m Strenath
Core #
Wet Strensth
Core # Unit Wt. flbl Mr- ( ksil
N/A 298.5
184.0
% Retention = 55
* Cracked, no integrity
TABLE 5: LABORATORY EVALUATION OF PAVE BOND SPECIAL CONTROL
SECTION CORES OBTAINED IN MARCH 1982
SILANE
Immersion Compression
Drv Strenath
Core # Unit Wt. f ~ c2 f Compressive Load (lb)
140.7 5240
141.2 5220
140.8 5100
140.9 5187
Strength = 413 psi
Wet Strenath
Core # Unit Wt. twcf) Comwressive Load Ilb)
Core #
Strength = 232 psi
% Retention = 56
Dynamic Stripping
Drv Strenath
Unit Wt. f ~ c1f
Wet Strensth
Core # Unit Wt. Mr (ksil
N/A *
N/A *
N/A 164.9
55.0
% Retention = 22.5
* Cracked, no integrity
TABLE 6: LABORATORY EVALUATION OF SILANE TEST SECTION CORES
OBTAINED IN MARCH 1982
CORE #
MCATION
M.P. or STA. R-L DEPTH
TABLE 7: LOCATION OF CORES TAKEN IN JANUARY/FEBRUARY,1985
CORE #
LOCATION
M.P. or STA. R-L DEPTH
NOTE: CORES No. 1 THRU 42 WERE TAKEN
SECTION. CORES 43 THRU 84 WERE
TEST SECTION.
FROM THE PBS CONTROL
TAKEN FROM THE SILANE
TABLE 7: CONTINUED
VOIDS ANALYSIS
Max. Density (Rice) =
Bulk Density of Core =
Air Voids -
Max Density (Rice) =
Bulk Density of -
(Marshall Plug)
Air Voids -
Max Density (Rice) =
Bulk Density of =
(Hveem Plug)
Air Voids -
Silane PBS Control
TABLE 8: VOIDS ANALYSIS OF PAVE BOND SPECIAL AND SILANE
CORES OBTAINED IN JANUARY 1985
AVG. BULK SP.GR.
POPULATION SIZE
STD. Dm.
AVG. DENSITY
POPULATION SIZE
STD. DEV.
MAX. THEORETICAL
DENSITY (RICE)
SILANE TEST PBS CONTROL
SECTION SECTION
145.9 pcf 149.0 pcf
42 41
1.0 1.3
157.5 pcf 157.4 pcf
% BITUMEN 5.24 8 5.16 %
VISCOSITY 9860 POISE 8200 POISE
AVG. STABILITY (CORE) 1587 lbs
POPULATION SIZE 3
STD. DEV. 233
AVG. FLOW (CORE)
POPULATION SIZE
STD. DN.
2100 lbs
3
321
AVG. STAB. (MARSHALL PLUG) 4960 lbs 4504 lbs
AVG. FLOW (MARSHALL PLUG) 11 10
BULK SP. GR. (MARSHALL PLUG) 2.427 2.428
AVG. DENSITY (MARSHALL PLUG) 151.2 pcf 151.3 pcf
AVG. HVEEM STAB. (CORE)
POPULATION SIZE
STD. DEV.
AVG. HVEEM COHESION. (CORE) 227 G/IN
POPULATION SIZE 3
STD. DEV. 5 6
AVG. HVEEM STAB. (REMOLDED) 5 6
POPULATION SIZE 3
STD. DEV. 4
TABLE 9: AVERAGE TEST RESULTS FOR LABORATORY EVALUATION OF
PAVE BOND SPECIAL AND SILANE CORES OBTAINED IN
JANUARY 1985
SILANE TEST PBS CONTROL
SECTION SECTION
AVG. HVEEM COHESION (REX.) 340 G/IN
POPULATION SIZE 3
STD. DEV. 28 67
BULK SP. GR. (HVEEM PLUG)
AVG. DENSITY (HVEEM PLUG)
AVG. IMC WET
AVG. IMC DRY
AVG. IMC RATIO
AVG. TENS. STRENGTH WET
AVG. TENS. STRENGTH DRY
AVG. TENS STRENGTH RATIO
AVG. MR DRY
POPULATION SIZE
STD. DEV.
MR W/D RATIO
TABLE 9: CONTINUED
439 PSI
839 PSI
42.0 PSI
198.7 PSI
490 PSI
759 PSI
82.1 PSI
236.2 PSI
WORKPLAN
CONSTRUCTION EXPERIMENTAL PROJECT - CATEGORY n
IG-I-40-3(28) W I L U A M S INTERSTATE FREEWAY UNIT I1
The HPR project HPR-PGl(19) Item 178 entitled "An Evaluation of
Chemical Coupling Agent" resulted in strong evidence that the use of organosilanes
were very effective in preventing stripping of as halt from aggregate by action of
moisture. To continue this work it IS reaueste a that a construction exLu~ e- ~r -ime-n~tal;- ~-- --
feature be approved on the above noted broject for full scale field evaluat~on of
silane-treated materials
Preliminary tests with the project asphalt and aggregate have indicated that
the silane will be effective in this specific system. Full scale laboratory testing is
underway and should be completed by October 8, 1981. It is proposed that this
construction experimental feature will consist of adding one quarter percent silane
by weight of the asphalt and placing the treated asphaltic concrete in a section of
pavement that will be approximately 2,000 feet in length and one paving lane wide.
This size of section should be adequate for field testing and evaluation. The
remainder of the project will be constructed usin the specified anti-strip agent and
that section directly adjacent to the experiment section will be used as a control
section.
3
The silane materials are being furnished at no cost for this test section but
there may be a minor charge by the contractor for handling. The exact description
of the construction experimental feature and any minor changes in the cost wll be
covered by a formal change order issued from the project level.
Evaluation of the experimental section will consist of obtaining field samples
(cores) and conducting laboratory tests which will include Immersion-Com ression,
Double Punch (Jimenez procedure) and resilient modulus evaluation. h e field
samples will include representative materials of both the experimental section and
the selected control section. Test results will be compared for evaluation.
Pavement samples will be obtained immediately after construction, at six months,
one year, and three years. Interim reports will be prepared after evaluation of
initial samples and at one year and a final report submitted after completion of the
three year tests. ATRC staff will be responsible for evaluation of the construction
experimental feature and the report preparation.

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ARIZONA DEPARTMENT OF TRANSPORTATION
REPORT NUMBER: FHWAIAZ EP 8101
LABORATORY AND FIELD
PERFORMANCE OF SILANE
ANTI-STRIP AGENT
Final Report
Prepared by:
Chaouki A. Gemayel
Arizona Transpoltation Research Center
November 1986
Prepared for:
Arizona Department of Transportation
206 south 17th Avenue
Phoenix, Arizona 85007
in cooperation with
U.S. Department of Transportation
Federal Highway Administration
The contents of this report reflect the views of the authors who are responsible for
the facts and the accura of the data presented herein. The contents do not
necessarily reflect the o2 cial' vie.ws or policies of the Arizona Department of
Transportation or the Federal Highway Administration. This report does not
constitute a standard, specification, or regulation Trade or manufacfarer's names
which may aP pear hereln are cited only because they are considered essential to the objectives o the report. The U. S. Government and the State of Arizona do not
endorse products or manufacturers.
TECHNICAL REPORT DOCUMENTATION PAGE
I. REPORT NO. 1 2. GOVERNMENT ACCESSION NO. I 3. RECIPIENT'S CATALOG NO. 1
AZ8101
4. TITLE AND SUBTITLE
LABORATORY AND FIELD PERFORMANCE OF SILANE ANTI-STRIP
AGENT
16. ABSTRACT
A previous ADOT research p r o j e c t resulted i n strong evidence t h a t the use o f I organo-silane as an asphalt a d d i t i v e was very e f f e c t i v e i n preventing s t r i p p i n g i n
asphalt concrete pavements. A t e s t section approximately 2800 ft long and 12 ft wide
incorporating a silane agent, Oow Corning 990, was placed on,the crossroad o f the east
I Williams T. I. on SR 64 between MP 185.3 and 185.7 i n October 1981 t o v e r i f y t h a t claim
Pave Bond Special (PBS) a n t i - s t r i p agent was used on the remaining portion o f the
- roadway. The PBS sections d i r e c t l y adjacent t o the silane t e s t section were designate
I as control sections.
I n January 1984, visual observations o f the silane t e s t section indicated t h a t the
pavement surface experienced s l i g h t r a v e l i n g throughout the section and moderate t o
severe raveling a t several l o c a l i z e d areas. The PBS control section was i n e x c e l l e n t 1 condition. The experimental t e s t section was overlayed by 1" ASCS i n October 1984
which prevented f u r t h e r f i e l d evaluation.
Laboratory tests were conducted on asphalt concrete samples obtained a t the time
I of c o n s t r u c t i o n and on cores taken from t h e s i l a n e and PBS sec t ions 5 months and 3 years after construction. The r e s u l t s showed t h a t the PBS t r e a t e d m a t e r i a l have
superior properties. However, several factors made the r e s u l t s questionable:
difference i n b u l k d e n s i t i e s between PBS and silane cores, clay material was observed I i n both mixtures and therefore increasing the moisture s u s c e p t i b i l i t y , and long delays
between the time the cores were d r i l l e d and the time they were tested.
Because o f the l i m i t e d f i e l d evaluation and the l i m i t a t i o n s on the v a l i d i t y o f the I laboratory r e s u l t s , no major conclusions can be drawn regarding t h e effectiveness o f
the silane i n preventing s t r i p p i n g .
17. KEY WORDS 18. DISTRIBUTION STATEMENT I Asphalt concrete, Stripping, Debonding, I A n t i - s t r i p aqent, Asohalt a d d i t i v e ,
5. REPORT DATE
November 1986
6. PERFORMING 0RGANIZAT;TIOH COO€
7 AUTHOR&)
Chaouki A. Gemayel
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arizona Transportation Research Center
Mail Drop 075R
206 South 17th Avenue; Phoenix, Arizona 85007
12. SWNSORING AGENCY NAME AND ADDRESS
Federal Highway Administration
234 North Central Avenue, Suite 330
Phoenix, Arizona 85004
. -
I Silane.
8. PERFORMING ORGANIZATION REPORT NQ
10. WORK UNIT NO.
11. CONTRACT OR GRANT NO.
HPR-PL-l(31) Item 116
I3.PIPE OF REWRT a PERIOD COVERED
Final Report
October 1981-November 1986
14. SPONSORING AGENCY CODE
- IS. SUPPLEMENTARY NOTES
EXPERIMENTAL PROJECT
A28101
LABORATORY AND FIELD PERFORMANCE OF
SILANE ANTI-STRIP AGENT
NOVEMBER 15,1986
PREPARED BY:
CHAOUKI A. GEMAYEL
TABLE OF CONTENTS
PAGE
TECHNICAL DOCUMENTATION ............................................................... i
TABLE OF CONTE.N...T...S.... ................................................................................................................................................................. ...... i.i. . LIST OF FIGURES n..i. LIST OF TABLES ................................................................................................ 1u INTRODUCTION ................................................................................................. 1
OBJECTIVE ........................................................................................................... 1
MECHANISMS OF STRIPPING ....................................................................... 2
PRODUCT DESCRIPTION ............................................................................... 2
CONSTRUCTION REPORT. ............................................................................3
PRODUCT EVALUATION PLAN ................................................................ 4 LABORATORY EVALUATION ...................................................................... 4
FIELD EVALUATION ........................................................................................ 6 CONCLUSIONS AND RECOMMENDATIONS. .......................................... 7
REFERENCES ...................................................................................................8...
APPENDICES
TEST SECTION PLANS .....................................................................A...1..
TEST SECTION PHOTOS ....................................................................B.. 1
LABORATORY DATA .........................................................................C.. 1
RESEARCH WORKPLAN ..................................................................... Dl
LIST OF FIGURES
FIGURE: PAGE
1 LOCATION OF THE EXPERIMENTAL TEST SECTION ......... A1
2 TYPICAL PAVEMENT CROSS SECTION ..................................... A2
3 SILANE TEST SECTION - LOOKING SOUTH
TABLE:
1
2
- - - ~ - - - - ---
FROM STA 3013+00 (JANUARY 1984) .......................................... B1
SILANE TEST SECTION - LOOKING SOUTH FROM STA 3015 + 00 (JANUARY 1984) .......................................... B1
PBS TEST SECTION - LOOKWG SOUTH FROM STA 3015 + 00 (JANUARY 1984) .......................................... B2
SILANE TEST SECTION - SURFACE TEXTWE (JANUARY 1984) .................................................................................. B2
SURFACE TEXTURE OF BOTH PBS (OUTSIDE LANE)
AND SILANE (INSIDE LANE) (JANUARY 1984) ....................... B3
1" ACSC OVERLAY - LOOKING NORTH FROM STA 3021 + 70 (AUGUST 1985) ............................................. B3
1" ACSC OVERLAY - LOOKING NORTH FROM STA 3033 + 87 (AUGUST 1985). ............................................ B4 1" ASCS OVERLAY - SURFACE TEXTURE. ................................ B4
LIST OF TABLES
LABORATORY EVALUATION OF SILANE
PRODUCTlON SAMPLES ..................................................................
LABORATORY EVALUATION OF PAVE BOND ~- - - - - SPECIAL (PBS) PRODUCTION SAMPLES ................................... C2
RESILIENT MODULUS EVALUATION OF PBS
AND SILANE PRODUCTION SAMPLES ...................................... C3
LOCATION 01 F CORES TAKEN IN MARCH 10, 1982 ................ C4
STAINED IN MARCH 1982 ......................... C6
LABORATORY EVALUATION OF PBS CONmOL
SECTION CORES OBTAINED IN MARCH 1982 ......................... U
LABORATORY EVALUATION OF SILANE TEST
SECTION CORES OE
LOCATION OF CORES TAKEN IN JANUARY /
FEBRUARY 1985 ................................................................................ C7
VOIDS ANALYSIS OF PBS AND SILANE CORES
.
OBTAINED IN JANUARY 1985 ........................................................ C9
AVERAGE TEST RESULTS FOR LABORATORY
EVALUATION OF P-B- S- -A-N -D SILANE CORES
. JANUARY 1985. .......................................................C 10
INTRODUCTION
An asphalt concrete pavement is inherently dependent upon the cohesive and
adhesive characteristics of the binder to hold it together. As a result, the bond between the
asphalt binder and the mineral aggregate is of special importance. It is critical that good
bond is developed during construction and maintained for the life of the pavement. Any
degree of loss of the asphalt-aggregate bond will result in a corresponding loss of pavement
performance in one manner or another. The strength of an asphalt concrete mvtture is a
result of the cohesive resistance of the binder, the adhesive bond between the binder and
the aggregate, aggregate interlock and frictional resistance between aggregate particles.
Under certain circumstances, an asphalt binder will separate from the aggregate, a
complex phenomenon known as debonding (commonly referred to as stripping).
Debonding is a function of the environmental conditions, traffic loading, binder and
aggregate characteristics, mixture properties and more. Even though a proper bonding of
the asphalt to the aggregate may take place during construction, debonding n still possible.
Water intrusion is the mechanism that will facihtate debonding by replacing the asphalt
coating on mineral aggregates. Since water will always be present m one form or another,
stripping is always a possibility. A brief review of the mechanisms of stripping is presented
in a subsequent section of this report.
Failure caused by stripping occurs in two stages: the first stage is the breaking of the
adhesive bond between the aggregate surface and the asphalt cement. The second stage is
failure of the pavement under traftic (1). If stri ping within the pavement becomes
excessive, loss of strength may result in excessive de? or mations caused by repeated loading.
Failure caused by stripping can also result in cracking and surface raveling of the
pavement.
Several methods have been used to limit the possibility of stripping. Some of the
more common methods are:
1. The addition of dry lime or portland cement in small percentages to the mix
or lime slurry treatment of mineral aggregate,
2. Precoating aggregates with bitumen prior to asphalt concrete production,
3. The addibon of selected natural mineral fillers,
4. Disallowance of lmown hydrophilic aggregates,
5. Washing, wasting or blending of aggregates, and
6. The addition of chemical anti-stripping agents.
AU of these methods, for one reason or another, are not always acceptable or
economical in every situation.
OBJECTIVE
A previous ADOT research project (HPR-PL-l(19) Item 178) entitled "An
Evaluation of Chemical Coupling Agents to Control Debonding of Asphalt from
Aggregates" resulted in strong evidence that the use of organo-silanes were very effective in
preventing stripping of asphalt by action of moisture (2). To complement the laboratory
investigabon, a construction experimental project was approved to establish a test section
of asphalt concrete utilizing an Amino functional organo-silane as a stripping preventative.
The urpose of the test section was to com are the performance of an organo-silane known as 8ow Coming 990 against Pave Bon Special, an asphalt additive commonly
utilized by ADOT.
B
MECHANISMS OF STRIPPING
Taylor and Khosla (1) indicated in their report that as many as five different
mechanisms have been blamed for the loss of bond between the aggregates and the asphalt
binder. A brief summary of those mechanisms is given below.
Detachement:
Detachement is the separation of an asphalt film from an aggregate surface by a
thin layer of water, with no obvious break in the asphalt film. The asphalt film can be s
peeled cleanly from the aggregate indicating a complete loss of adhesion
Displacement:
In this mechanism, water penetrates to the aggregate through a break in the asphalt
film. This break can be caused by incomplete coating of the aggregate initially, by film
rupture, or by pinholes in the asphalt film which can form after coating dusty aggregates.
Spontaneous Emulsification: -
Water and asphalt combine to form an inverted emulsion where asphalt represents
the continuous phase and water represents the discontinuous phase. The presence of
emulsifiers such as mineral clays and some asphalt additives can aggravate further the
stripping problem.
Pore Pressure:
Pore pressure has been suggested as a mechanism of strippin& in .hig h void mixes
where water may circulate freely through interconnected voids. Dens caoon due to traffic
may entrap some water in the voids. Further traffic can cause high water pressure which
could lead to the loss of adhesion between the aggregates and the binder.
Hydraulic Scouring:
This mechanism is only applicable to surface courses. Stripping results from the
action of traffic tires on a saturated pavement surface. This causes water to be pressed
down in front of the tire and immediately sucked away from the pavement behind the tire. -
It has been indicated that stripping begins at the bottom of the asphalt bound layer
and progresses upward to the top of the layer. This is true because the lower portion of the
layer is under tension. This could lead to the rupture of the asphalt film causing water
intrusion and therefore increasing the possibility of stripping.
PRODUCT DESCRIPTION
Pave Bond Special:
Pave Bond Special (PBS) is a registered trade name of a Carstab Corporation
product. It is marketed as an asphalt additive to prevent debonding. This product was
extensively used by ADOT prior to the modification of the asphalt concrete mix design
procedures in 1982. Currently this product is an approved anti-strip agent for asphalt
concrete friction courses.
Dow Coming 990:
Silane coupling agents were first introduced to improve the water resistance of
reinforced plastics. It was soon observed that they also imparted significant improvement
to initial properties of laminates (3). Hydrophilic mineral surfaces were used in preparing
composites with organic polymers and silane was used to improve the bond. The similarity
between the polymer-glass systems and the pavement materials was noted and it was felt
that silanes may have the potential to increase the bond between asphalt and mineral
aggregate surfaces.
The original product used in the initial laboratory study under HPR-PL-l(19) Item
178 was known as Dow 2-6020. It was a registered trade name of DOW Corning. It was
primarily used as a coupling agent for the resin and plastic industry (3). It is a low viscosity
liquid of the type: aminoalkyl functional silane with the molecular formula
(CH30)3SiCH2NHCH2CH2NH2. It is only one member of one subclass of the much
larger group of functional organo-silane coupling agents.
Dow 2-6020 was not initial1 marketed for the highway industry. However, the
same product was later renamed to &ow Corning 990 and identified as an asphalt additive.
According to the manufacturer's information, Dow Corning 990 additive is effective as an
anti-stripping agent at low concentrations (0.5 - 1.0 lb per 1000 lb bitumen). The exact
quantity added depends on the nature of the particular asphalt mix. A uniform blend is
important and can be accomplished by metering the additive directly into the mixing system
of an asP halt plant or by adding it to filled tank trucks and recirculating through a bypass system or at least 20 minutes for each of the 1000 gallons of asphalt. A third option
available to the contractor is the pretreatment of the aggregate with the additive.
CONSTRUCTION REPORT
The experimental test section is located on the crossroad of the East Williams T.I.
on SR 64 between mile posts 185.3 and 185.7. The test section was established by a change
order (C.O. # 28) on project I-IG-40-3 (28). This construction experimental feature
consisted of adding two-tenths of one percent silane by weight of the asphalt and placing
the treated asphalt concrete in a section of pavement that is approximately 2800 feet in
length. Two test areas were constructed:
1. Section A is located on the northbound lanes between station 3027+40 and
station 592+72 (3046+36.62=593+55.63). The 1980 feet long by 12 feet
wide section was placed in the inside travel lane near the centerline of the
highway.
2. Section B is located on the southbound shoulder and a part of the outside
travel lane between station 3013+73.62 and Station 3021 +70. The width of
the section varied between 8 and 14 feet (8 ft between sta 3013+73.62 and
sta 3016+50,8 to 14 ft taper section between sta 3016+50 and 3018+00, and
14 ft between 3018+00 and 3021+70).
The location of the test section was selected in the Williams area because of the
past history of stripping problems along 1-40 in the Williams, Flagstaff and surrounding
areas. Stripping has been reported in pavement shortly after the completion of
construction activities even when anti-strip agents were used.
The project location and geomerty are shown in Fig. 1 and 2. The size of the section
was adequate for field testing and evaluation. The remainder of the project was
constructed using PBS, the anti-strip agent originally specified in the construction project.
The sections containing PBS and which are directly adjacent to the silme test sections were 7
designated as control sections.
A total of 872.85 tons of asphalt concrete containing the silane was used for this
experiment. The silane treated material was placed in the top 2 inch lift of the surface
course. The pavement structural components are also shown in Fig. 2. The application
rate of the silane was ap roximately 0.20 % silane by weight of the asphalt cement. The
test sections were place 8 on October 14, 1981. There were no problems associated with
placing and compacting the pavement. .
i
Although it was suggested by research ersonnel that three ranges of silane concentrations be tested (0.05 %, 0.15%, and 0. 2 % by the wei ht of asphalt), only one
could be estimated (0.20%) due to problems with metering the ow concentration of the
silane additive.
f
PRODUCT EVALUATION PLAN
The research workelan submitted by the Arizona Transportation Research Center
(ATRC) to the Federal Jibghway Administration (FHWA) indicated that the evaluation of
the experimental section will consist of conducting laboratory testing on the treated asphalt
concrete in both the experimental and control section. A copy of the workplan is enclosed
in appendix D.
The tests were to be conducted during construction (i.e. sampled material prior to
placement and compaction) and at several stages during the life of the pavement. In
addition, the evaluation included visual determination of stripping (if any).
?
LABORATORY EVALUATION
The laboratory testing rogram consisted of the evaluation of properties that would
reflect the moisture susceptitility of the asphalt concrete mixture. These properties
included the strength retention ratios as estimated from the immersion-compression and
dynamic stripping tests, conventional mix desigo properties (i.e. Marshall and Hveem
parameters), and the determination of the asphalt brnder viscosity to study the effect of the
additives on the aging of the binder. The laboratory evaluation consisted of a series of tests
that were conducted at three stages within the service life of the pavement. Tests were
performed on the treated mixture sampled during construction and on cores obtained from
the field 5 months later and 3 years later. 4
Material Sampled During Construction:
The tests listed below were conducted on both the PBS and silane field mixtures
obtained prior to compaction:
A) Immersion-compression, Marshall stability and flow, Hveem stability and
cohesion, and viscosity of extraction binder.
B) Resilient modulus on Hveem compacted specimens when
conditioning with the hydraulic device. The test is continued undt'r faainludr ea. fter
Part A of this program was completed on January 22,1982. Part B was delayed until
July 9, 1982 due to equipment malfunctions. The results of both parts are shown in Tables
1 to 3.
Cores Obtained After Five Months:
Field samples were obtained on March 10, 1982 from the experimental and control
sections. Twenty cores were taken at random in each section. The location of the cores
are included in Table 4. The tests conducted on these sam~lesin cluded the immersion-compression,
resilient modulus tests on original and cohditioned cores, and visual
determination of stripping. The results of these tests are presented in Tables 5 and 6.
Cores Obtained After Three Years:
Field samples were taken again after the pavement had been in service for three
years. A total of eighty four cores were drilled. Some of the cores were drilled next to the
1982 locations and the remaining were selected at random in both the control and
experimental sections. The location of the cores are included in Table 7. The coring
operation began in January 9-10,1985 and was completed in February 12-14,1985.
A comprehensive testing program was performed on the cores selected from both
the control and the experimental section The tests included the resilient modulus
evaluation, Hveem and Marshall tests on both the original and remolded cores and binder
extraction on both PBS and silane mixtures. The test program was completed in April 24,
1986. The results are listed in Tables 8 and 9.
Discussion of Laboratory Results:
The results of tests performed on the samples obtained from the field during
construction showed a slight difference between the properties of both the silane and PBS
treated mixtures. The silane mixture showed slightly higher stability values which might be
attributed to the difference in the average bulk density. Although the silane mixture
exhibited a higher wet strength, the strength retention ratio obtained from the immersion-compression
test was a little higher for the PBS samples.
Higher resilient modulus values were obtained for the dry specimens containing the
silane treatment. The specimens containing both the PBS and silane treated material
cracked after conditioning. Note that the resilient modulus tests were delayed for
approximately six months after the completion of the first part of the testin rogram. In
addition, a substantial amount of clay was observed throughout the mix. erefore the
results should be reviewed with caution.
+Fl
The results of the tests conducted on the cores obtained in March of 1982 are listed
in Tables 5 and 6. Visual observation during testing revealed obvious weakening of cores
after exposure to moisture. The weakening was observed as cracking and small eruptions
in the cores. Closer examination of the cores showed clay balls to be the cause of the
distress. The presence of clay was also noted in the production samples which were tested
earlier. The influence of the clay on the results of the tests conducted on the cores limits
the validity of any conclusions drawn on the performance of the two additives.
The results indicated that the PBS cores showed superior properties to the silane
cores. Strength retention values from both the immersion compression and dynamic
stripping were higher for the PBS specimens.
Similar visual observations were made on the cores obtained in 1985. Clay material
was observed throughout the mix. Another factor limiting the validity of using these test
results to compare the performance of the two additives is the long delay experienced z
between obtaining the cores and the completion of the testing program (approx. 15
months). To complicate the matter further, the cores showed consistently higher densities
in the PBS section. The results of the tests indicated that the PBS have superior properties.
It is not known to what extent the difference in the densities had on these results. Voids
calculations showed higher air voids in the silane section. Air voids in both the silane and
PBS cores were higher than the expected design air voids as obtained by the Marshall and
Hveem methods. Note that the higher air voids in the mixture, the higher chance for water
intrusion and therefore the higher moisture susceptibility of the mixture. This could
explain some of the difference between the properties of both PBS and silane mixtures. i
Absolute viscosity tests conducted on extraction binders from cores obtained in
January 1985 indicated the silane agent increases the viscosity of the asphalt binder. This
increase in viscosity may result in a decrease in the flexibility of the pavement and
therefore a decrease in the pavement serviceability due to possible fatigue cracking.
In conclusion, although the PBS cores indicated higher stripping resistance as shown
by the higher strength retention ratios for tests conducted on the original mixtures as well
as the cores, it is hard to rank one product over another. The difficulty arises from
different factors which include the presence of clay material in both mixtures, the -
difference in densities between the PBS and silane cores, and the delay in testing the cores
after obtaining them.
FIELD EVALUATION
The project suffered a delay in inspection reportin until January, 1984 when the
test section was visuall inspected and photographed (Fig. f -7). The control sections were in excellent condition (kg8.) with no apparent visual distresses. 7
Fine particle erosion was observed in the silane test areas. Slight raveling was
visible throughout test area A The fine particles were eroded leaving the coarse
aggregates exposed (Fig. 6 & 7). On the other hand, test area B showed more localized
raveling of higher severity than that observed in section A (Fig. 3 & 4). The distressed
areas in test area B were located near the construction joint between the silane and the
PBS test sections.
The original avement design required an 8 1/2 in. thick asphalt concrete surface course and 1/2 in. tll'c k asphalt concrete friction course (ACFC) be placed on to of the A
10 in. awegate base. The friction course was to be placed the following fall. If owever,
the friction course was later deleted and the thickness of the surface course was reduced by
1/2 in. (C.O. # 24 project I-IG-40-3(28)). This action was taken by the Materials section
because of problems experienced with the open-graded friction courses in a freeze-thaw
environment (4). These problems were more visible in areas that were not exposed to
sunlight because of ice accumulation. This condition is typical of that existing in the
premises of the experimental project.
The reduced thickness was replaced by a 1 in. thick asphalt concrete dense mix
overlay with a 1/2 " maximum aggregate size. The overlay was placed under project I-IG-
40-3(58) which was completed in October of 1984. Portland cement was used in the 1 inch
overlay to prevent stripping.
The presence of the overlay revented ATRC's personnel from visually comparing
the strip ing potential of the contro ? and experimental sections. A visual field ins ection
in August of 1985 to evaluate the condition of the pavement al t'e r the
placed (Figure 9-11). No signs of distress were observed other than two
transverse cracks extending across the fu!l width of the pavement at the beginning and end
of the test section.
No major conclusions could be drawn for the purpose of comparison between the
experimental and control section based on the available field inspection reports.
CONCLUSIONS AND RECOMMENDATIONS
The results of laboratory tests conducted at different stages during the three year
evaluation period suggest that PBS has su erior properties. However, the reliability of
these results is questionable due to several !ac tors: a difference in the bulk densities of the
cores obtained from the test sections was experienced with PBS cores consistently
exhibiting higher densities, clay material was observed in all mixtures increasing the
moisture susce tibility, and long delays were experienced between the time the cores were
obtained and t g e time they were tested.
The field evaluation indicated a sli ht to moderate raveling of the fine particles in
the silane test sections. The long term pe ormance of the additives could not be obtained
since both sections were overlayed.
r!
In conclusion, the corn arison of the PBS and silane anti-strip additives are
inconclusive and would not &ct current ADOT spedcations. At the present time,
ADOT uses liquid anti-strip agents on ACFC mixes. Several products are included on the
Material's ap roved products list. Portland cement and lime are currently used to control
stripping in cf ense mixtures. Usually, 1 to 2 % by weight of the mineral aggregates are
added to original mixes and 1 % by weight of virgin and salvaged material are added to
recycled asphalt concrete.
Further laboratory and field testing will be required before recommendations could
be made as to whether or not this product should be included in the anti-strip agents'
approved list.
REFERENCES
1) Joseph A. Di Vito and Gene R. Moms, "Silane Pretreatment of Mineral Aggregate
to Prevent Stripping in Flexible Pavements" A Paper Presented at the Annual
Meeting of the Transpo.tation Research Board - Washington, D.C.; January 1982. i
2) M. A Taylor and N. P. Khosla, "Stripping of Asphalt Pavements: State of the Art",
Transportation Research Record 911, Transportation Research Board -
Washlngton,D.C.; 1983.
3) Plueddemann, E. P ., "Mechanism of Adhesion of Coatings Through Reactive
Silanes", Journal of Paint Technology, March 1970.
4) Personal communications with Mr. Donald Dorman of ADOTs District 4.
APPENDIX
$7
-3
STA. 3013 + 73.62
EAST WILLIAMS
CROSSROAD
4 EAST WILLIAMS CROSSROAD
END SILANE
SECTION "0"
STA. 3021 + 70
END SILANE
STA. 592 + 75
STA. 5 8 4 + 75
END I" AC ( 1/21
FIGURE 1: LOCATION OF THE EXPERIMENTAL TEST SECTION
-Al-
SILANE TREATED
MIXTURE (2" LIFT) 7 OVERLAYED 10,1984
8" A.C.
10" S. M.
DETAIL A-A
I W' varies from 8 t o 14 f e e t
FIGURE 2: TYPICAL PAVEMENT CROSS SECTION
SILANE
Marshall Method Bulk Density Stability Flow
(PCf (lbs)
Hveem Method Bulk Density, pcf Stability Cohesion
A 146.2 26 81
B 145.9 2 7 105
C 146.5 -2 9 -107
AVg . 146.2 2 7 98
Extraction Results Gradation
Sieve % Pass
% Bitumen
Abs. Viscosity @ 140'~.
4.96
3440 poises
Immersion compression Results*
D r v Strensth. vsi Wet Strensth. vsi % Retention
70 234 33
Ava. Density of Svecimens 142.5 pcf
* Upon failure of specimens, the interior and exterior
was observed to have a substantial amount of clay
present throughout the mix.
TABLE 1: LABORATORY EVALUATION OF SILANE PRODUCTION SAMPLES
PAVE BOND SPECIAL
Marshall Method Bulk Density Stability Flow
(pcf (lbs)
A 145.1
B 146.1
C 145.2
avg . 145.6
Hveem Method Bulk Density, pcf Stability Cohesion
A 146.9
B 145.8
C 145.9
avg . 146.2
Extraction Results Gradation
Sieve % Pass
1" 100
3/4 9 9
1/ 2 86
3/8 80
1/4 6 9
4 6 3
8 4 6
10 4 1
16 32
30 24
40 19
5 0 13
100 6
200 4.1
% Bitumen 5.47
A~S. viscosity @ 140'~. 2860 poises
Immersion Compression Results*
D m Strensth. wsi Wet Strenath. ~ s i % Retention
555 217 39
Ava. Densitv of Swecimens 141.5 pcf
* Upon failure of specimens, the interior and exterior
was observed to have a substantial amount of clay
present throughout the mix.
TABLE 2: LABORATORY EVALUATION OF PAVE BOND SPECIAL
PRODUCTION SAMPLES
SILANE
-
i
PAVE BOND SPECIAL
*liveem compacted
NOTE: All specimens cracked after conditioning.
TABLE 3: RESILIENT MODULUS EVALUATION OF PAVE BOND SPECIAL
AND SILANE PRODUCTION SAMPLES
CORE #
rnCATION
M.P. or STA. R-L
592+75 R5
3043+38 L8
3042+56 L6
3041+86 L5
3040+61 L11
3039+61 L6
3938+61 L4
3038+16 L7
3037+00 L7
3034+00 L5
3014+00 R i 3
3014+50 R12
3015+00 R14
3016+50 R12
3017+00 R11
3017+50 R12
3018+00 R12
3019+00 R12
3020+00 R12
3021+00 R12
529+75 L12
3043+36 R8
3042+56 R12
3041+86 R14
3040+61 R14
3034+61 R14
3038+61 R16
3038+16 R15
3037+00 R15
3034+00 R14
3014+00 L13
3014+50 L12
3015+00 L12
3016+50 L13
3017+00 L12
3017+50 L10
3018+00 L10
3019+00 L12
3020+00 L15
3021+00 L15
DEPTH
10.2
9.0
9.5
9.5
8.5
10.5
9.5
9.0
9.5
9.7
9.5
9.0
9.6
9.5
9.6
9.3
9.6
10.5
9.3
10.5
9.0
9.5
9.0
9.0
9.0
9.5
9.5
9.5
9.5
9.0
9.7
9.5
9.0
9.8
10.0
10.1
10.0
9.5
9.5
9.0
NOTE: CORES No. 1 THRU 20 WERE TAKEN FROM THE SILANE TEST
SECTION. CORES 21 THRU 40 WERE TAKEN FROM THE PBS
CONTROL SECTION.
TABLE 4: LOCATION OF CORES TAKEN I N MARCH 10,1982
PAVE BOND SPECLQL
Core #
Core #
Immersion Compression
Unit Wt. f~cfl_ Comvressive Load I lb)
146.0 6420
144.2 6280
142.0 5480
144.1 6060
Strength = 482 psi
Wet Strenuth
Unit Wt. fvcf) Comuressive Load f lbl_
143.0 3780
143.5 4480
145.6 -5860
144.0 4707
Strength = 375 psi
% Retention = 78
Dynamic Stripping
D m Strenath
Core #
Wet Strensth
Core # Unit Wt. flbl Mr- ( ksil
N/A 298.5
184.0
% Retention = 55
* Cracked, no integrity
TABLE 5: LABORATORY EVALUATION OF PAVE BOND SPECIAL CONTROL
SECTION CORES OBTAINED IN MARCH 1982
SILANE
Immersion Compression
Drv Strenath
Core # Unit Wt. f ~ c2 f Compressive Load (lb)
140.7 5240
141.2 5220
140.8 5100
140.9 5187
Strength = 413 psi
Wet Strenath
Core # Unit Wt. twcf) Comwressive Load Ilb)
Core #
Strength = 232 psi
% Retention = 56
Dynamic Stripping
Drv Strenath
Unit Wt. f ~ c1f
Wet Strensth
Core # Unit Wt. Mr (ksil
N/A *
N/A *
N/A 164.9
55.0
% Retention = 22.5
* Cracked, no integrity
TABLE 6: LABORATORY EVALUATION OF SILANE TEST SECTION CORES
OBTAINED IN MARCH 1982
CORE #
MCATION
M.P. or STA. R-L DEPTH
TABLE 7: LOCATION OF CORES TAKEN IN JANUARY/FEBRUARY,1985
CORE #
LOCATION
M.P. or STA. R-L DEPTH
NOTE: CORES No. 1 THRU 42 WERE TAKEN
SECTION. CORES 43 THRU 84 WERE
TEST SECTION.
FROM THE PBS CONTROL
TAKEN FROM THE SILANE
TABLE 7: CONTINUED
VOIDS ANALYSIS
Max. Density (Rice) =
Bulk Density of Core =
Air Voids -
Max Density (Rice) =
Bulk Density of -
(Marshall Plug)
Air Voids -
Max Density (Rice) =
Bulk Density of =
(Hveem Plug)
Air Voids -
Silane PBS Control
TABLE 8: VOIDS ANALYSIS OF PAVE BOND SPECIAL AND SILANE
CORES OBTAINED IN JANUARY 1985
AVG. BULK SP.GR.
POPULATION SIZE
STD. Dm.
AVG. DENSITY
POPULATION SIZE
STD. DEV.
MAX. THEORETICAL
DENSITY (RICE)
SILANE TEST PBS CONTROL
SECTION SECTION
145.9 pcf 149.0 pcf
42 41
1.0 1.3
157.5 pcf 157.4 pcf
% BITUMEN 5.24 8 5.16 %
VISCOSITY 9860 POISE 8200 POISE
AVG. STABILITY (CORE) 1587 lbs
POPULATION SIZE 3
STD. DEV. 233
AVG. FLOW (CORE)
POPULATION SIZE
STD. DN.
2100 lbs
3
321
AVG. STAB. (MARSHALL PLUG) 4960 lbs 4504 lbs
AVG. FLOW (MARSHALL PLUG) 11 10
BULK SP. GR. (MARSHALL PLUG) 2.427 2.428
AVG. DENSITY (MARSHALL PLUG) 151.2 pcf 151.3 pcf
AVG. HVEEM STAB. (CORE)
POPULATION SIZE
STD. DEV.
AVG. HVEEM COHESION. (CORE) 227 G/IN
POPULATION SIZE 3
STD. DEV. 5 6
AVG. HVEEM STAB. (REMOLDED) 5 6
POPULATION SIZE 3
STD. DEV. 4
TABLE 9: AVERAGE TEST RESULTS FOR LABORATORY EVALUATION OF
PAVE BOND SPECIAL AND SILANE CORES OBTAINED IN
JANUARY 1985
SILANE TEST PBS CONTROL
SECTION SECTION
AVG. HVEEM COHESION (REX.) 340 G/IN
POPULATION SIZE 3
STD. DEV. 28 67
BULK SP. GR. (HVEEM PLUG)
AVG. DENSITY (HVEEM PLUG)
AVG. IMC WET
AVG. IMC DRY
AVG. IMC RATIO
AVG. TENS. STRENGTH WET
AVG. TENS. STRENGTH DRY
AVG. TENS STRENGTH RATIO
AVG. MR DRY
POPULATION SIZE
STD. DEV.
MR W/D RATIO
TABLE 9: CONTINUED
439 PSI
839 PSI
42.0 PSI
198.7 PSI
490 PSI
759 PSI
82.1 PSI
236.2 PSI
WORKPLAN
CONSTRUCTION EXPERIMENTAL PROJECT - CATEGORY n
IG-I-40-3(28) W I L U A M S INTERSTATE FREEWAY UNIT I1
The HPR project HPR-PGl(19) Item 178 entitled "An Evaluation of
Chemical Coupling Agent" resulted in strong evidence that the use of organosilanes
were very effective in preventing stripping of as halt from aggregate by action of
moisture. To continue this work it IS reaueste a that a construction exLu~ e- ~r -ime-n~tal;- ~-- --
feature be approved on the above noted broject for full scale field evaluat~on of
silane-treated materials
Preliminary tests with the project asphalt and aggregate have indicated that
the silane will be effective in this specific system. Full scale laboratory testing is
underway and should be completed by October 8, 1981. It is proposed that this
construction experimental feature will consist of adding one quarter percent silane
by weight of the asphalt and placing the treated asphaltic concrete in a section of
pavement that will be approximately 2,000 feet in length and one paving lane wide.
This size of section should be adequate for field testing and evaluation. The
remainder of the project will be constructed usin the specified anti-strip agent and
that section directly adjacent to the experiment section will be used as a control
section.
3
The silane materials are being furnished at no cost for this test section but
there may be a minor charge by the contractor for handling. The exact description
of the construction experimental feature and any minor changes in the cost wll be
covered by a formal change order issued from the project level.
Evaluation of the experimental section will consist of obtaining field samples
(cores) and conducting laboratory tests which will include Immersion-Com ression,
Double Punch (Jimenez procedure) and resilient modulus evaluation. h e field
samples will include representative materials of both the experimental section and
the selected control section. Test results will be compared for evaluation.
Pavement samples will be obtained immediately after construction, at six months,
one year, and three years. Interim reports will be prepared after evaluation of
initial samples and at one year and a final report submitted after completion of the
three year tests. ATRC staff will be responsible for evaluation of the construction
experimental feature and the report preparation.